This invention relates to a conveyor system for the bulk transfer of bar-shaped articles, in particular cigarettes, and more particularly relates to those conveyors which directly connect one or more cigarette manufacturing machines to one or more cigarette packaging machines.
For reasons of simplicity, the present description will relate to the case of a single packaging machine fed by two manufacturing machines.
In said conveyor systems, the known means for supporting and conveying cigarettes are constituted by belts which define overall an assembly of channels along which the cigarettes disposed horizontally and piled one on the other are fed with continuous motion in a direction transverse to their longitudinal axes.
These channels, which lead from the manufacturing machines by way of paths generally comprising horizontal, vertical, curved and sometimes inclined portions, open into a hopper which feeds the cigarettes to the packaging machine.
A condition for the correct operation of the conveying system and consequently of the entire installation, is that the quantity of cigarettes present at any time in said channels is such as to prevent the feed to the packaging machine from becoming interrupted, and to prevent the cigarettes from becoming disposed in a disordered manner particularly in the descending portions of the conveyor.
A further condition for correct operation is that no pressure arises within the bulk of cigarettes flowing along said channels such as to cause build-up and damage to the cigarettes.
In order for these conditions to be continuously satisfied, known conveyor systems comprise, in the path of said channels, control and detection devices sensitive to any variation in the cigarette quantity caused for example by the different operating rates of the manufacturing machines and packaging machine, by the different efficiencies of said machines, and by faults in said conveyor system.
Said control devices are disposed at critical positions in the conveyor system (for example at its inlet, in the passage zones from one channel to another and at the point where several channels converge), and suitably adjust the speed of said belts in response to any deviation in the cigarette quantity from the preset or normal value.
More precisely, if the cigarette quantity falls below said value, the conveyor belts controlled by said control devices undergo a speed change relative to the normal speed such as to prevent the formation of empty spaces or gaps in the bulk of cigarettes.
In the same manner, if the cigarette quantity increases beyond said value, the conveyor belts are controlled by said control devices to a speed such as to prevent any build-up along the conveyor system and any dangerous pressure inside the bulk of cigarettes.
In conclusion, said control devices control the conveyor belt speed in such a manner that said conditions for correct operation are satisfied as the throughput of the conveyor system varies.
In order to ensure constant speed to the packaging machine even during said throughput variation, or more generally during any unbalance between the working rate of the manufacturing machines and packaging machine, known conveyor systems comprise at least one variable volume store which opens into the channels connecting said machines.
Control devices of the aforesaid type are therefore also disposed at the mouth of said store, and control its operation in such a manner as to keep the installation in perfect balance.
More particularly, the store receives either a cigarette delivery command or an absorption command depending upon whether the requirement of the packaging machine is respectively greater or less than the operating rate of the manufacturing machines.
From the aforegoing, it is apparent that said control devices govern the correct operation of the conveyor system and of the entire installation, and ensure delicate treatment of the cigarettes during all transfer operations.
The known art uses mechanical control devices of high sensitivity. In these, even very small variations in the cigarette quantity in the controlled zones are converted into movements of mechanical parts in direct contact with the cigarettes, and then into commands fed to the conveyor system drive means.
For example, control devices are known which are located inside substantially vertical wells disposed in positions where two or more channels of the conveyor system converge.
Variations in the cigarette quantity at these converging zones are converted into variations in the cigarette level inside the wells, and thus into vertical sliding of mechanical means in the control devices.
The same category comprises control devices which instead of detecting level variations detect pressure variations consequent on variations in the cigarette quantity in the controlled zone.
In this latter case, the mechanical elements disposed in contact with the cigarettes define wall portions of said channels, and can, for example, be in the form of flexible strips of plastics or fabric material, flexible belts mobile in the same direction as the motion of the bulk of cigarettes, or plates swivel-mounted on respective supports.
It is apparent that in all the cases considered, during the various stages of their control along the conveyor path the cigarettes are subjected to pressure and sometimes to friction and rolling, which can alter their structure and cause escape of tobacco.